Transmission and vehicle having transversely mounted transmission and engine arranged in axial direction thereof

ABSTRACT

A vehicle includes an engine, a pair of side frames extending along a vehicle body in a front-rear direction of the vehicle, a transmission adapted to be axially connected with the engine and adapted to be transversely mounted on the vehicle body, includes an input shaft, an output shaft, a first counter shaft, a second counter shaft, a first gear mechanism, a second gear mechanism, a third gear mechanism, and a transmission case, wherein the first and second gear mechanisms are arranged relatively close to the engine, the third gear mechanism is arranged more remote from the engine than the second gear mechanism, the first counter shaft is arranged above the input shaft and the second counter shaft, and the transmission case forms a cut-out portion at an upper portion of a back wall portion of the transmission case.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2007-235824, filed on Sep. 11, 2007, the entire contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a vehicle having an engine and a transmission that are connected to each other in an axial direction thereof and that are transversely mounted on the vehicle relative to a vehicle body.

BACKGROUND

In order to downsize a transmission and increase output torque, for example, a transmission apparatus disclosed in JP2002-70960A, adapted to a front-engine front-drive type vehicle to which an engine and a transmission connected in an axial direction thereof are transversely mounted, includes an input shaft, two counter shafts and plural shift stage gear sets that are arranged in parallel to each other between the input shaft and each of the counter shafts, thereby shortening length of the transmission apparatus in an axial direction thereof without reducing number of shift stages. A transmission 1 illustrated in FIG. 5 has substantially the same structure as the transmission apparatus disclosed in the second embodiment of JP2002-70960A. As illustrated in FIG. 5, an input shaft 3 a, first counter shaft 3 b, a second counter shaft 3 c and a reverse shaft 3 d are arranged in parallel to each other within a transmission case 2. The first counter shaft 3 b and the second counter shaft 3 c are connected to output shafts 8 a and 8 b via reduction gear set 6 a, 6 b and 6 c and a differential mechanism 7. A first forward movement gear switching unit 4A forming a 1st shift stage and a 2nd shift stage and a second forward movement gear switching unit 4B forming a 3rd shift stage and a 4th shift stage are arranged to connect the input shaft 3 a and the first counter shaft 3 b. The second forward movement gear switching unit 4B is positioned farther away from an engine 10 than the first forward movement switching unit 4A. A third forward movement switching unit 4C forming a 5th shift stage and a 6th shift stage is arranged between the input shaft 3 a and the second counter shaft 3 c so as to be located at a position substantially corresponding to the position where the second forward movement gear switching unit 4A is arranged, in an axial direction of the input shaft 3 a. Further, a reverse movement gear switching mechanism 4D forming a reverse shift stage is arranged between the input shaft 3 a, the second counter shaft 3 c and the reverse shaft 3 d so as to be located at a position substantially corresponding to the position where the first forward movement gear switching unit 4A is provided, in the axial direction of the input shaft 3 a. A back wall portion 2 a of the transmission case 2, substantially corresponding to an area where input shaft 3 a, the first counter shaft 3 b and the second counter shaft 3 c are arranged orthogonally relative to the back wall portion 2 a, is formed to have a flat surface.

FIG. 6 schematically illustrates a forward portion of the vehicle, viewed in a lateral direction thereof, to which a driving unit is transversely mounted at the forward portion of a vehicle body. The driving unit is a unit in which the transmission 1 disclosed in JP2002-70960A is connected to the engine 10 in an axial direction thereof. As illustrated in FIG. 6, the driving unit is positioned between a pair of side frames 9 extending along both sides of the vehicle body in a front-rear direction thereof. In order to prevent the side frames 9 from interfering with a front axle, forward portions of the side frames 9 are curved upwardly. Hence, as illustrated in FIG. 6, the side frame 9 at the left side in FIG. 6 extends along immediate left of an upper portion of the back wall portion 2 a of the transmission case 2 in the front-rear direction of the vehicle.

In order to increase collision safety and vehicle stiffness, a cross-section of each of the side frames 9 needs to be enlarged and a shape of each of the side frames 9 needs to be linearized. The side frames 9 a having the enlarged cross-sectional area and the linearized shape are illustrated with chain double-dashed lines in FIG. 6. As is evident from the position of the side frames 9 a having the enlarged cross-section and illustrated with the chain double-dashed lines in FIG. 6, the side frame 9 a at the left side in FIG. 6 interferes with an upper left portion of the back wall portion 2 a of the transmission case 2, and the side frame 9 a at the right side in FIG. 6 is positioned closer to the engine 10. Hence, the driving unit having axially connected engine 10 and transmission 1 may have difficulties when being transversely mounted on the vehicle body. A case where the driving unit, in which the engine and the transmission are connected in the axial direction thereof, is adapted to the front-engine front-drive type vehicle is described above. However, as is the case with the transmission adapted to the front-engine front-drive type vehicle described above, in a case where a similar driving unit is adapted to a rear-engine rear-drive type vehicle, the driving unit in which the transmission 1 and the engine 10 are connected in an axial direction thereof may have difficulties when being transversely mounted on the vehicle body because of the similar reasons explained above.

The transmission apparatus disclosed in JP2002-70960A suggests a modified transmission apparatus in which a portion of the back wall of the transmission case positionally corresponding to the second counter shaft is arranged closer to the engine, compared to a portion of the back wall positionally corresponding to the first counter shaft, by eliminating one shift stage. However, in the transmission apparatus disclosed in JP2002-70960A, the portion on the back wall, corresponding to the second counter shaft and positioned closer to the engine than other portions of the back wall, is positioned at lower portion of the transmission case, thus resulting in creating a dead space at the back wall portion of the transmission case. Hence, even with the modified transmission apparatus disclosed in JP2002-70960A, the driving unit may have difficulties when being transversely mounted on the vehicle.

A need thus exists for a vehicle which is not susceptible to the drawback mentioned above.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a vehicle includes an engine, a pair of side frames provided at the vehicle so as to extend along both sides of a vehicle body in a front-rear direction of the vehicle, a transmission adapted to be axially connected with an engine and adapted to be transversely mounted on a vehicle body, including, an input shaft adapted to be rotatably driven by the engine, an output shaft connected to a driving wheel, a first counter shaft arranged in parallel to the input shaft and connected to the output shaft, a second counter shaft arranged in parallel to the input shaft and connected to the output shaft, a first gear mechanism between the input shaft and the first counter shaft, the first gear mechanism having a first gear set, a second gear set and a first switching clutch provided between the first and second gear sets to selectively establish a power transmission path between the input shaft and the first counter shaft via either the first gear set or the second gear set, a second gear mechanism between the input shaft and the second counter shaft, the second gear mechanism having a third gear set, optionally a fourth gear set and a second switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the third gear set, or if present, the fourth gear set, a third gear mechanism between the input shaft and the second counter shaft, the second and third gear mechanisms extending in parallel with one another between the input shaft and the second counter shaft, the third gear mechanism having a fifth gear set, optionally a sixth gear set and a third switching clutch provided between the fifth and sixth gear sets to establish a power transmission path established between the input shaft and the second counter shaft via the fifth gear set, or if present, the sixth gear set, and a transmission case 12 supporting and covering most of the input shaft, the first counter shaft, the second counter shaft, the output shaft, the first gear mechanism, the second gear mechanism and the third gear mechanism, wherein the first gear mechanism and the second gear mechanism are arranged relatively close to the engine, the third gear mechanism is arranged at a position more remote from the engine than the second gear mechanism, and the first counter shaft is arranged above the input shaft and the second counter shaft, a driving gear of the second gear set, serves also as the driving gear of the third gear set and is axially aligned with the ends of the second and third gear sets closer to the engine, and a driving gear of the first gear set is arranged at an axial distance from the engine substantially corresponding to the axial location of the third switching clutch, and wherein the transmission case includes a back wall portion formed with a first back wall portion corresponding to the second gear mechanism and the third gear mechanism and a second back wall portion corresponding to the first gear mechanism and located closer to the engine than the first back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion, and wherein the transmission is connected to the engine and transversely mounted on the vehicle body so that one of the pair of the side frames extending along the both sides of the vehicle body in the front-rear direction thereof extends through the cut-out portion.

According to another aspect of the present invention, a transmission adapted to be axially connected with an engine and adapted to be transversely mounted on a vehicle body, includes an input shaft adapted to be rotatably driven by the engine, an output shaft connected to a driving wheel, a first counter shaft arranged in parallel to the input shaft and connected to the output shaft, a second counter shaft arranged in parallel to the input shaft and connected to the output shaft, a first gear mechanism between the input shaft and the first counter shaft, the first gear mechanism having a first gear set, a second gear set and a first switching clutch provided between the first and second gear sets to selectively establish a power transmission path between the input shaft and the first counter shaft via either the first gear set or the second gear set, a second gear mechanism between the input shaft and the second counter shaft, the second gear mechanism having a third gear set, optionally a fourth gear set and a second switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the third gear set or, if present, the fourth gear set, a third gear mechanism between the input shaft and the second counter shaft, the second and third gear mechanisms extending in parallel with one another between the input shaft and the second counter shaft, the third gear mechanism having a fifth gear set, optionally a sixth stage gear set and a third switching clutch provided between the fifth and sixth gear sets to selectively establish a power transmission path between the input shaft and the second counter shaft via the fifth gear set or, if present, the sixth gear set, and a transmission case 12 supporting and covering most of the input shaft, the first counter shaft, the second counter shaft, the output shaft, the first gear mechanism, the second gear mechanism and the third gear mechanism, wherein the first gear mechanism and the second gear mechanism are arranged relatively close to the engine, the third gear mechanism is arranged at a position more remote from the engine than the second gear mechanism, and the first counter shaft is arranged above the input shaft and the second counter shaft, a driving gear of the second gear set serves also as the driving gear of the third gear set and is axially aligned with the ends of the second and third gear sets closer to the engine, and a driving gear of the first gear set is arranged on the input shaft at an axial distance from the engine substantially corresponding to the axial location of the third switching clutch, and wherein the transmission case includes a back wall portion formed with a first back wall portion corresponding to the second gear mechanism and the third gear mechanism and a second back wall portion corresponding to the first gear mechanism and located closer to the engine than the first back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein:

FIG. 1 is a view schematically illustrating an entire structure of an example of a transmission adapted to a vehicle in which axially connected engine and transmission is transversely mounted;

FIG. 2 is a view schematically illustrating the transmission viewed from the left side in FIG. 1;

FIG. 3 is a view of a portion of the vehicle, viewed in a transverse direction thereof, at which the axially connected engine and transmission is transversely mounted;

FIG. 4 is a view illustrating a second embodiment of the transmission illustrated in FIG. 1;

FIG. 5 is a view schematically illustrating an entire structure of an example of a conventional transmission; and

FIG. 6 is a sectional view of the vehicle, viewed in lateral direction thereof, at which the axially connected engine and the conventional transmission is transversely mounted.

DETAILED DESCRIPTION First Embodiment

A first embodiment of a transmission and a vehicle, to which the transmission and an engine connected in an axial direction thereof are transversely mounted, will be described below in accordance with FIGS. 1 to 3 of the attached drawings. FIG. 3 schematically illustrates a sectional view of a forward portion of the vehicle, viewed in a transverse direction thereof, in a case where the axially connected engine and transmission of the first embodiment is adapted to a front-engine front-drive type vehicle. An engine 10 and a transmission 11, connected with each other in the axial direction thereof, are transversely mounted between forward portions of left and right side frames 13 that serve as primary strength members and that extend along the both side portions of a vehicle body in a front-rear direction of the vehicle. The transmission 11 is arranged at the left of the engine 10 in FIG. 3. A cut-out portion 12 b, which will be described below, is formed at an upper portion of a back wall portion 12 a of a transmission case 12. The forward portion of the left side frame 13 of the left and right side frames 13, whose forward portions are upwardly curved for avoiding interference with a front axle, extends through the cut-out portion 12 b formed at the upper portion of the back wall portion 12 a of the transmission case 12.

As illustrated in FIGS. 1 and 2, the transmission 11 includes an input shaft 15 rotatably driven by the engine 10, an output shaft 19 connected to driving wheels (not shown), first and second counter shafts 16 and 17 and a reverse shaft 18 that are arranged in parallel to the input shaft 15 and that are connected to the output shaft 19 via a reduction gear set 28 a, 28 b, 28 c and 28 d, a first forward movement gear switching unit 20A (a first gear mechanism) arranged between the input shaft 15 and the first counter shaft 16, a second forward movement gear switching unit 20B (a second gear mechanism) and a third forward movement gear switching unit 20C (a third gear mechanism) each of which is arranged between the input shaft 15 and the second counter shaft 17, a reverse movement gear switching unit 20D (a reverse movement gear mechanism) arranged between the input shaft 15 and the reverse shaft 18, and the transmission case 12. The transmission case 12 supports the input shaft 15, the first and second counter shaft 16 and 17, the reverse shaft 18, the output shaft 19, the first, second, and third forward movement gear switching units 20A, 20B, 20C and a reduction gear set 28 a, 28 b, 28 c and 28 d, most of which are accommodated therewithin. The reduction gear set 28 a, 28 b, 28 c and 28 d is arranged at a position which is the closest to the engine 10 among the gear sets within the transmission case 12. The first, second and third forward movement gear switching units 20A, 20B and 20C are positioned so as to be further away from the engine 10 than the reduction gear set 28 a, 28 b, 28 c and 28 d.

As illustrated in FIGS. 1 and 3, the transmission 11 is arranged at one side of the engine 10 so as to be connected therewith in the axial direction of the engine 10. The transmission case 12 is fixed to the engine 10. A left end portion and a middle portion of the input shaft 15 in FIG. 1 is rotatably supported at the transmission case 12, and a right end portion of the input shaft 15 is connected to a crank shaft (not shown) of the engine 10 via a clutch (not shown). Both ends of each of the first counter shaft 16 and the second counter shaft 17 and the reverse shaft 18 are rotatably supported at the transmission case 12. The output shaft 19 is formed with a first shaft 19 a and a second shaft 19 b that are coaxially connected via a differential mechanism 29 arranged within the transmission case 12. The first and second shafts 19 a and 19 b are rotatably supported by the transmission case 12. Further, each outer end portion of each of the first and second shafts 19 a and 19 b is connected to the corresponding driving wheel via a joint and a drive shaft (not shown). The smaller reduction gears 28 a, 28 b and 28 c, fixed at the first and second counter shafts 16 and 17 and the reverse shaft 18, respectively, engage with the larger reduction gear 28 d, having a larger diameter than the reduction gears 28 a, 28 b and 28 c and provided at the differential mechanism 29, thereby connecting the first and second counter shafts 16 and 17 and the reverse shaft 18 to the output shaft 19. ‘Small’, as used in the reduction small gears 28 a, 28 b and 28 d, does not refer to specific size thereof, but rather because sizes of the reduction gears 28 a, 28 b, and 28 d are smaller than the reduction gear 28 d. Similarly, ‘large’, as used in the reduction large gear 28 d, does not refer to a specific size thereof, but rather because a size of the reduction gear 28 d is larger than other reduction gears 28 a, 28 b and 28 c. Additionally, as illustrated in FIG. 2, the first counter shaft 16 and the reverse shaft 18 are positioned above the input shaft 15 and the second counter shaft 17.

As illustrated in FIG. 1, the first forward movement gear switching unit 20A is arranged at a position relatively close to the engine 10. The first forward movement gear switching unit 20A forms a 1st shift stage and a 2nd shift stage, and includes two pairs of gear sets arranged between the input shaft 15 and the first counter shaft 16, i.e. a 1st shift gear set (first gear set) 21 a, 21 b and a 2nd shift stage gear set (second gear set) 22 a, 22 b, and a first switching clutch 30A. The 1st shift stage gear set includes the driving gear 21 a and the driven gear 21 b, and the 2nd shift stage gear set includes the driving gear 22 a and the driven gear 22 b. The first switching clutch 30A is arranged between the 1st shift stage gear set 21 a, 22 b and the 2nd shift stage gear set 22 a, 22 b, and establishes a power (torque) transmission path established by each of the 1st shift stage gear set 12 a, 22 b and the 2nd shift stage gear set 22 a, 22 b between the input shaft 15 and the first counter shaft 16. The driving gear 21 a of the 1st shift stage gear set 21 and 21 b and the driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b are fixed at the input shaft 15, and the driven gear 21 b of the 1st shift stage gear set 21 a and 21 b and the driven gear 22 b of the 2nd shift stage gear set 22 a and 22 b are rotatably provided at the first counter shaft 16. The first switching clutch 30A is provided between the driven gears 21 b and 22 b, and selectively connects either one of the driven gears 21 b and 22 b with rotation of the first counter shaft 16.

A known synchromesh mechanism is adapted to the first switching clutch 30A. The first switching clutch 30A incorporates therein a clutch hub L fixed at the first counter shaft 16, a sleeve M spline-engaged with an outer periphery of the clutch hub L so as to be movable in an axial direction of the first counter shaft 16, and engaging members S1 and S2 that are integrally formed at the driven gears 21 b and 22 b, respectively and that are spline-engageable with the sleeve M. When the sleeve M of the first switching clutch 30A is shifted towards the driven gear 21 b by means of a manually or automatically operated shift fork N from a neutral position illustrated in FIG. 1, the sleeve M is spline-engaged with the engaging member S1, and the driven gear 21 b of the 1st shift stage gear set 21 a and 21 b is connected to the rotation of the first counter shaft 16. As a result, the 1 st shift stage is established. Further, when the sleeve M is shifted towards the driven gear 22 b by means of the shift fork N from the position where the 1st shift stage is established, firstly the engaging member S1 is disengaged from the sleeve M, and the sleeve M is returned to the neutral position. When the sleeve M is shifted further towards the driven gear 22 b, the sleeve M is spline-engaged with the engaging member S2, and the driven gear 22 b of the 2nd shift stage gear set 22 a and 22 b is connected to the rotation of the first counter shaft 16. As a result, the 2nd shift stage is established. When the sleeve M is shifted towards the driven gear 21 b from the position where the 2nd shift stage is established, the sleeve M is returned to the neutral position.

As is the case with the first forward movement gear switching unit 20A, the second forward movement gear switching unit 20B is arranged at a position relatively close to the engine 10. The third forward movement gear switching unit 20C is arranged at the position more remote from the engine 10 than the second forward movement gear switching unit 20B. The second forward movement gear switching unit 20B forms a 3rd shift stage and a 4th shift stage, and includes a 3rd shift stage gear set (third gear set) 23 a, 23 b and a 4th shift stage gear set (fourth gear set) 24 a, 24 b, both of which are arranged between the input shaft 15 and the second counter shaft 17, and a second switching clutch 30B arranged between the 3rd and second 4th stage gear sets. The 3rd shift stage gear set includes the driving gear 23 a and the driven gear 23 b, and the 4th shift stage gear set includes the driving gear 24 a and the driven gear 24 b. The second forward movement gear switching unit 20B is structured substantially the same as the first forward movement gear switching unit 20A. When a sleeve M of the second switching clutch 30B is shifted towards the driven gear 23 b of the 3rd shift stage gear set 23 a and 23 b from a neutral position illustrated in FIG. 1, the 3rd shift stage is established by the substantially same manner as, for example, the 2nd shift stage is established. When the sleeve M is shifted towards the driven gear 24 b of the 4th shift stage gear set 24 a and 24 b from the position where the 3rd shift stage is established, the sleeve M is returned to the neutral position. When the sleeve M is further shifted towards the driven gear 24 b from the neutral position, the 4th shift stage is established. Further, when the sleeve M is shifted towards the driven gear 23 b from the position where the 4th shift stage is established, the sleeve M is returned to the neutral position.

The third forward movement gear switching unit 20C forms a 5th shift stage and a 6th shift stage, and includes a 5th shift stage gear set (fifth gear set) 25 a, 25 b and a 6th shift stage gear set (sixth gear set) 26 a, 26 b, both of which are arranged between the input shaft 15 and the second counter shaft 17, and a third switching clutch 30C arranged between the 5th and 6th shift stage gear sets. The 5th shift stage gear set includes the driving gear 25 a and the driven gear 25 b, and the 6th shift stage gear set includes the driving gear 26 a and the driven gear 26 b. The third forward movement gear switching unit 20C is structured substantially the same as the first and second forward movement gear switching units 20A and 20B. When a sleeve M of the third switching clutch 30C is shifted towards the driven gear 25 b of the 5th shift stage gear set 25 a and 25 b from a neutral position illustrated in FIG. 1, the 5th shift stage is established by the substantially same manner as, for example, the 1st shift stage is established. When the sleeve M is shifted towards the driven gear 26 b of the 6th shift stage gear set 26 a and 26 b from the position where the 5th shift stage is established, the sleeve M is returned to the neutral position. When the sleeve M is further shifted towards the driven gear 26 b from the neutral position, the 6th shift stage is established. Further, when the sleeve M is shifted towards the driven gear 25 b from the position where the 6th shift stage is established, the sleeve M is returned to the neutral position.

The driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b, arranged at the position relatively close to the engine 10 at the first forward movement gear switching unit 20A, is fixed at the input shaft 15 and serves also as the driving gear 23 a of the 3rd shift stage gear set 23 a and 23 b arranged at the position relatively close to the engine 10 at the second forward movement gear switching unit 20B. The driving gear 21 a of the 1st shift stage gear set 21 a and 21 b, arranged at the position more remote from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b, is fixed at the input shaft 15 at the position substantially corresponding to the third switching clutch 30C of the third forward movement gear switching unit 20C in the axial direction thereof. That is to say, the driving gear 21 a of the 1st shift stage gear set 21 a and 21 b is fixed at the input shaft 15 so as to be arranged between the driving gear 25 a of the 5th shift stage gear set 25 a, 25 b and the driving gear 26 a of the 6th shift stage gear set 26 a, 26 b of the third forward movement gear switching unit 20C.

As illustrated in FIGS. 1 and 2, the reverse movement gear switching unit 20D includes a reverse gear set 27, arranged between the input shaft 15, the first counter shaft 16 and the reverse shaft 18, and a reverse movement switching clutch 30D that is configured to establish a power transmission path established by the reverse gear set 27 between the input shaft 15 and the reverse shaft 18. The reverse gear set 27 is formed with a driving gear 27 a, an idler gear 27 b and a driven gear 27 c. The driving gear 27 a and the idler gear 27 b serve also as the 1st shift stage gear set 21 a and 21 b, respectively, arranged further away from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b. Further, the driven gear 27 c is rotatably supported at the reverse shaft 18 and is engaged with the idler gear 27 b (driven gear 21 b) so that the driven gear 27 c is connectable with rotation of the reverse shaft 18 by means of the reverse movement switching clutch 30D arranged at a position relatively close to the engine 10 at the reverse movement gear switching unit 20D. The reverse movement switching clutch 30D has substantially the same structure as the first switching clutch 30A except that the reverse movement switching clutch 30D includes only an engaging member SR fixed at the driven gear 27 c, arranged at one side of the reverse movement switching clutch 30D, in an axial direction of the reverse shaft 18. When a sleeve M of the reverse movement switching clutch 30D is shifted towards the driven gear 27 c from a neutral position illustrated in FIG. 1 by means of a shift fork N, the sleeve M is spline-engaged with the engaging member SR, and the driven gear 27 c of the reverse gear set 27 is connected to the rotation of the reverse shaft 18. As a result, a reverse shift stage is established. When the sleeve M is shifted towards the reduction gear 28 c from the position where the reverse shift stage is established, the sleeve M is disengaged from the engaging member SR, and the reverse shift stage is cancelled.

In the above-described first embodiment, the first forward movement gear switching unit 20A and the second forward movement gear switching unit 20B are arranged at the positions relatively close to the engine 10 within the transmission case 12, and the third forward movement gear switching unit 20C is arranged more remote from the engine 10 than the second forward movement gear switching unit 20B. The 1st shift stage gear set 21 a and 21 b, arranged more remote from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b, are arranged between the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b of the third forward movement gear switching unit 20C, in the axial direction of the input shaft 15. Further, the 1st shift stage gear set 21 a and 21 b serve also as the driving gear 27 a and the idler gear 27 b, respectively, of the reverse movement gear switching unit 20D arranged further away from the engine 10 than the reverse movement switching clutch 30D. Therefore, a farthest end portion of each of the first forward movement gear switching unit 20A and the reverse movement gear switching unit 20D from the engine 10 is arranged closer to the engine 10 than a farthest end portion of the third forward movement gear switching unit 20C from the engine 10 in the axial direction of the input shaft 15. Further, the first counter shaft 16, at which the driven gear 21 b of the first forward movement gear switching unit 20A serving also as the idler gear 27 b of the reverse gear set 27 is provided, and the reverse shaft 18, at which the driven gear 27 c is provided, are arranged above the input shaft 15 and the second counter shaft 17 at which the third forward movement gear switching unit 20C is provided, as illustrated in FIG. 2. Therefore, as illustrated in FIGS. 1 and 3, the transmission case 12, located at the opposite side of the engine 10, is formed to have the first back wall portion 12 a 1 corresponding to the second and third forward movement gear switching units 20A and 20B and the second back wall portion 12 a 2 corresponding to a portion of the first forward movement gear switching unit 20A and the reverse movement gear switching unit 20D arranged at the first counter shaft 16 and the reverse shaft 18, wherein the second back wall portion 12 a 2 is located closer to the engine 10 than the first back wall portion 12 a 1 formed below the second back wall portion 12 a 2. As a result, the transmission case 12 forms the cut-out portion 12 b at the upper portion of the back wall portion 12 a.

In the above-described embodiment, the transmission case 12 forms the cut-out portion 12 b at the back wall portion 12 a thereof. Hence, as illustrated in FIG. 3, in a case where the transmission 11 and the engine 10 are arranged in the axial direction thereof so as to be integrally connected with each other and then the integrally and axially connected transmission 11 and engine 10 is transversely mounted at the forward portion of the vehicle body, the upwardly curved forward portion of one of the right and left side frames 13, serving as the strength member, is arranged so as to extend through the cut-out portion 12 b of the transmission case 12. As a result, even in a case where axially connected transmission 11 and the engine 10 of the first embodiment is adapted to a vehicle having side frames having the enlarged cross-sectional shapes and linearized shapes, as illustrated in FIG. 3, one of the side frames 13 is prevented from interfering with the transmission case 12 because the one of the side frames 13 extends through the cut-out portion 12 b of the transmission case 12, compared to a case where the conventional transmission 1 interferes with one of the side frames 9 a having the enlarged cross-sectional shapes and linearized shapes when the conventional transmission 1 and the engine 10 are axially connected and transversely mounted on the vehicle body, as illustrated in FIG. 6. Hence, the axially connected transmission 11 and engine 10 is transversely mountable on the vehicle body without causing interference between one of the side frames 13 and the transmission case 12.

In the above-described first embodiment, the driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b, arranged at the position relatively close to the engine 10 at the first forward movement gear switching unit 20A, is fixed at the input shaft 15 and serves also as the driving gear 23 a of the 3rd shift stage gear set 23 a and 23 b, arranged at the position relatively close to the engine 10 at the second forward movement gear switching unit 20B. As a result, one of plural gears provided at the input shaft 15 is eliminated, compared to the conventional transmission apparatus. Therefore, the structure of the transmission 11 is simplified, and length of the input shaft 15 and the counter shaft 17 are shortened, which results in shortening length of the transmission case 12 in the axial direction of the input shaft 15.

Second Embodiment

A second embodiment of an example of a modified transmission 11′ will be described below in accordance with FIG. 4. The modified transmission 11′ has substantially the same structure as the transmission 11 described in the above-mentioned first embodiment except that a reverse movement gear switching unit 20D′ of the modified transmission 11′ has a different structure from the reverse movement gear switching unit 20D of the above-described transmission 11 of the first embodiment. Therefore, differences between the modified transmission 11′ and the above-described transmission 11 will be mainly described below. In the modified transmission 11′, a second idler gear 27 b 2, whose diameter is smaller than a first idler gear 27 b 1 of a reverse gear set 27A, is integrally and axially formed at the first idler gear 27 b 1 so as to be positioned between the first idler gear 27 b 1 and the engaging member S1 of the first switching clutch 30A, so that a driving gear 27 c′ is engaged with the second idler gear 27 b 2. Further, a reverse movement switching clutch 30D′ of the modified transmission 11′ is arranged at the position more remote from the engine 10 than the driven gear 27 c′, and further, the reverse movement switching clutch 30D′ is arranged at the reverse shaft 18 so as not to be positioned farther away from the engine 10 than the 1st shift stage gear set 21 a and 21 b in the axial direction of the input shaft 15. The modified transmission 11′ is structured the same as the transmission 11 of the first embodiment except for the reverse movement gear switching unit 20D. Hence, detailed explanations on structures of other parts of the modified transmission 11′ will be omitted.

As is the case with the above-described transmission 11 of the first embodiment, as illustrated in FIG. 4, the transmission case 12, located at the opposite side of the engine 10, is formed to have the first back wall portion 12 a 1 corresponding to the second and third forward movement gear switching units 20A and 20B and the second back wall portion 12 a 2 corresponding to a portion of the first forward movement gear switching unit 20A and the reverse movement gear switching unit 20D arranged at the first counter shaft 16 and the reverse shaft 18, wherein the second back wall portion 12 a 2 is located closer to the engine 10 than the first back wall portion 12 a 1 arranged below the second back wall portion 12 a 2. As a result, the transmission case 12 forms the cut-out portion 12 b at the upper portion of the back wall portion 12 a. As a result, even in a case where axially connected transmission 11′ and the engine 10 of the first embodiment is adapted to a vehicle having side frames having the enlarged cross-sectional shapes and linearized shapes, as illustrated in FIG. 3, one of the side frames 13 is prevented from interfering with the transmission case 12 because the one of the side frames 13 extends through the cut-out portion 12 b of the transmission case 12, compared to a case where the conventional transmission 1 interferes with one of the side frames 9 a having the enlarged cross-sectional shapes and linearized shapes when the conventional transmission 1 and the engine 10 are axially connected and transversely mounted on the vehicle body. Hence, the axially connected transmission 11′ and engine 10 is transversely mountable on the vehicle body without causing interference between one of the side frames 13 and the transmission case 12.

In the second embodiment of the modified transmission 11′, because the second idler gear 27 b 2, which is integrally formed with the first idler gear 27 b 1 in the axial direction of the first counter shaft 16 and is engaged with the driven gear 27 c′, is formed to have a smaller diameter than the first idler gear 27 b 1 (i.e. a reduction gear ratio of the reverse gear set 27A between the input shaft 15 and the reverse shaft 18 is determined on the basis of a gear ratio between the driving gear 27 a′ and the first idler gear 27 b 1 and a gear ratio between the second idler gear 27 b 2 and the driven gear 27 c′), a diameter of the driven gear 27 c′ may be reduced in a case where the reduction gear ratio between the input shaft 15 and the reverse shaft 18 of the second embodiment is set as the same level of the reduction gear ratio between the input shaft 15 and the reverse shaft 18 of the first embodiment in which the idler gear 27 b is engaged with the driving gear 27 a and the driven gear 27 c (i.e. the reduction gear ratio of the reverse gear set 27 between the input shaft 15 and the reverse shaft 18 is determined on the basis of a gear ratio between the driving gear 27 a and the driven gear 27 c). As a result, a protruding amount of the transmission case 12 because of the reverse movement gear switching unit 20D′ may be reduced, which allows the axially and integrally connected modified transmission 11′ and engine 10 to be easily transversely mounted on the vehicle body. Alternatively, by integrally and axially combining two gears whose diameters differ from each other as a idler gear, the reduction gear ratio between the input shaft 15 and the reverse shaft 18 is changeable to any desired reduction gear ratio without talking mountability of the axially connected modified transmission 11′ and engine 10 to the vehicle body into consideration.

In the second embodiment of the modified transmission 11′, the reverse movement switching clutch 30D′ is provided at the position more remote from the engine 10 than the driven gear 27 c′, however, the reverse movement switching clutch 30D′ may be arranged at a position closer to the engine 10 relative to the driven gear 27 c′. In a case where the reverse movement switching clutch 30D′ is arranged at the position closer to the engine 10 relative to the driven gear 27 c′, a rear end portion of the reverse movement gear switching unit 20D′ is positioned further closer to the engine 10 than the rear end portion of the first forward movement gear switching unit 20A, compared to the case where the reverse movement switching clutch 30D′ is arranged further away from the engine 10 than the driven gear 27 c′. In the case where the reverse movement switching clutch 30D′ is arranged at the position closer to the engine 10 relative to the driven gear 27 c′, a portion of the second back wall portion 12 a 2 corresponding to the reverse movement switching clutch 30D′ of the second back wall portion 12 a 2 of the back wall portion 12 a located more remote from the engine 10 is positioned closer to the engine 10, which results in enlarging the cut-out portion 12 b formed at the upper portion of the back wall portion 12 a.

The first and second embodiments describe the transmission having the reverse movement gear switching unit 20D (20D′). However, the present invention described in the first and second embodiments is adaptable to a transmission not having a reverse movement gear switching unit. Even in a case where the present invention is adapted to the transmission not having the reverse movement gear switching unit, most of the effects and advantages described above in the first and second embodiments will be achieved.

Further, in the transmission 1 (11′) of the first and second embodiments, the first forward movement gear switching unit 20A includes the 1st shift stage gear set 21 a, 21 b, the 2nd shift stage gear set 22 a, 22 b and the first switching clutch 30A that is provided therebetween and established the power transmission path established by each of the 1st shift stage gear set 21 a, 21 b and the 2nd shift stage gear set 22 a, 22 b between the input shaft 15 and the first counter shaft 16, the second forward movement gear switching unit 20B includes the 3rd shift stage gear set 23 a, 23 b, the 4th shift stage gear set 24 a, 24 b and the second switching clutch 30B that is provided therebetween and establishes the power transmission path established by each of the 3rd shift stage gear set 23 a, 23 b and the 4th shift stage gear set 24 a, 24 b between the input shaft 15 and the second counter shaft 17, and the third forward movement gear switching unit 20C includes the 5th shift stage gear set 25 a, 25 b, the 6th shift stage gear set 26 a, 26 b and the third switching clutch 30C that is provided therebetween and establishes the power transmission path established by each of the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b between the input shaft 15 and the second counter shaft 17. Accordingly, the transmission 11 (11′) is structured to have six shift stages which is a maximum number of shift stages for a transmission having three forward movement gear switching units. Hence, output torque of the transmission 11 (11′) is increased. The present invention is not limited to the above-described first and second embodiments, but one or more of the first, second and third forward movement gear switching units 20A, 20B and 20C may include only one forward movement shift stage gear set.

In the above-described first and second embodiments, the third forward movement gear switching unit 20C is formed with the 5th shift stage gear set (fifth forward movement shift stage gear set) 25 a, 25 b, the 6th shift stage gear set (sixth forward movement shift stage gear set) 26 a, 26 b, and the third switching clutch 30C provided therebetween. The 1st shift stage gear set (first forward movement shift stage gear set) 21 a and 21 b, arranged at the input shaft 15 so as to substantially correspond to the third switching clutch 30C in the axial direction of the input shaft 15, is positioned between the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b. The present invention is not limited to the above-described structure, but the third forward movement gear switching unit of the transmission may include only one forward movement shift stage gear set, for example, the 6th shift stage gear set 26 a and 26 b may be removed from the third forward movement gear switching unit 20C of the above-described embodiments. In the case where the third forward movement gear switching unit includes only one forward movement shift stage gear set, the 1 shift stage gear set (first forward movement shift stage gear set) 21 a and 21 b is positioned closer to the engine 10 than the 5th shift stage gear set 25 a and 25 b. As is the case with the above-described embodiments, even in the case where the third forward movement gear switching unit 20C includes only one forward movement shift stage gear set, the stepwisely depressed cut-out portion 12 b is formed at the upper back wall portion 12 a of the transmission case 12, and the effects and advantages described above are achievable.

In the above-described first and second embodiments, the first forward movement shift stage gear set is assigned as the 1st shift stage gear set 21 a and 21 b, the second forward movement shift stage gear set is assigned as the 2nd shift stage gear set 22 a and 22 b, the third forward movement shift stage gear set is assigned as the 3rd shift stage gear set 23 a and 23 b, the fourth forward movement shift stage gear set is assigned as the 4th shift stage gear set 24 a and 24 b, the fifth forward movement shift stage gear set is assigned as the 5th shift stage gear set 25 a and 25 b, and the sixth forward movement shift stage gear set is assigned as the 6th shift stage gear set 26 a and 26 b. However, each shift stage may be assigned at any desired forward movement shift stage gear set arranged at the positions illustrated in FIGS. 1 and 4.

Further, in the above-described first and second embodiments, the case where the axially connected transmission 11 (11′) and engine 10 is adapted to the front-engine front-drive type vehicle is described above. The present invention is not limited to be adapted to the front-engine front-drive type vehicle, but the present invention is also adaptable to a rear-engine rear-drive type vehicle.

Accordingly, the first forward movement gear switching unit 20A and the second forward movement gear switching unit 20B are arranged relatively close to the engine 10 within the transmission case 12, and the third forward movement gear switching unit 20C is arranged more remote from the engine 10 than the second forward movement gear switching unit 20B. The first counter shaft 16 is arranged above the input shaft 15 and the second counter shaft 17. The driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b arranged relatively close to the engine 10 at the first forward movement gear switching unit 20A is fixed at the input shaft 15 and serves also as the driving gear 23 a of the 3rd shift stage gear set 23 a and 23 b arranged relatively close to the engine 10 at the second forward movement gear switching unit 20B. Further, the driving gear 21 a of the 1st shift stage gear set 21 a and 21 b, arranged more remote from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b, is provided at the input shaft 15 at the position substantially corresponding to the position where the third switching clutch 30C of the third forward movement gear switching unit 20C is provided, in the axial direction of the input shaft 15. As a result, the transmission case 12, located at the opposite side of the engine 10, is formed to have the first back wall portion 12 a 1 corresponding to the second and third forward movement gear switching units 20A and 20B and the second back wall portion 12 a 2 corresponding to the portion of the first forward movement gear switching unit 20A, wherein the second back wall portion 12 a 2 is located closer to the engine 10 than the first back wall portion 12 a 1 arranged below the second back wall portion 12 a 2. As a result, the transmission case 12 forms the cut-out portion 12 b at the upper portion of the back wall 12 a. By adapting the above-structured transmission 11 (11′), the transmission 11 (11′) and the engine 10 are connected in the axial direction thereof, and the axially connected transmission 11 (11′) and engine 10 is transversely mounted on the vehicle body so that one of the side frames 13, extending along the both sides of the vehicle body in the front-rear direction thereof, extends through the cut-out portion 12 b of the transmission case 12. As a result, even in a case where axially connected transmission 11 (11′) and the engine 10 of the first embodiment is adapted to a vehicle having side frames having the enlarged cross-sectional shapes and linearized shapes, as illustrated in FIG. 3, one of the side frames 13 is prevented from interfering with the transmission case 12 because the one of the side frames 13 extends through the cut-out portion 12 b of the transmission case 12, compared to a case where the conventional transmission 1 interferes with one of the side frames 9 a having the enlarged cross-sectional shapes and linearized shapes when the conventional transmission 1 and the engine 10 are axially connected and transversely mounted on the vehicle body, as illustrated in FIG. 6. Hence, the axially connected transmission 11 (11 ′) and engine 10 is transversely mountable on the vehicle body without causing the interference between one of the side frames 13 and the transmission case 12. Further, as the driving gear 22 a of the 2nd shift stage gear set 22 a and 22 b of the first forward movement gear switching unit 20A serves also as the driving gear 23 a of the 3rd shift stage gear set 23 a and 23 b of the second forward movement gear switching unit 20B, one of the driving gears is eliminated. As a result, the structure of the transmission 11 (11′) is simplified and the transmission 11 (11′) is downsized. Moreover, as the driving gear 21 a of the 1st shift stage gear set 21 a and 21 b of the first forward movement gear switching unit 20A is provided at the input shaft 15 at the position substantially corresponding to the position where the third switching clutch 30C of the third forward movement gear switching unit 20C is provided, in the axial direction of the input shaft 15, the lengths of the second and third forward movement gear switching units 20B and 20C, which are arranged in parallel to each other in the axial direction of the input shaft 15, are not elongated. Hence, the protruding amount of the first back wall portion 12 a 1 of the back wall 12 a of the transmission 11 (11′) from the engine 10 is not increased.

According to the embodiments, the transmission 11 (11′) transversely mounted on the vehicle includes the reverse movement gear switching unit 20D (20D′) including the reverse shaft 18 arranged in parallel to the input shaft 15 and connected to the output shaft 19, the reverse gear set 27 (27A) provided between the input shaft 15 and the reverse shaft 18 and the reverse movement switching clutch 30D (30D′) establishing the power transmission path established by the reverse gear set 27 (27A) between the input shaft 15 and the reverse shaft 18, wherein the 1st shift stage gear set 21 a and 22 b arranged more remote from the engine 10 than the 2nd shift stage gear set 22 a and 22 b is set as the gear set for the low speed shift stage, the reverse gear set 27 (27A) includes the driving gear 27 a (27 a′) provided at the input shaft 15, the driven gear 27 c (27 c′) rotatably supported at the reverse shaft 18 and connected to the rotation of the reverse shaft 18 by means of the reverse movement switching clutch 30D (30D′) and the idler gear 27 b (27 b 1 /27 b 2) rotatably supported at the first counter shaft 16 and engaged with the driving gear 27 a (27 a′) and the driven gear 27 c (27 c′), wherein the driving gear 27 a (27 a′) and the idler gear 27 b (27 b 1) of the reverse gear set 27 (27A) serve also as the driving gear 21 a and the driven gear 21 b of the 1st shift stage gear set provided at the first forward movement gear switching unit 20A, respectively, arranged more remote from the engine 10 than the 2nd shift stage gear set.

Accordingly, the transmission 11 (11′) further includes the reverse shaft 18 arranged in parallel to the input shaft 15 and connected to the output shaft 19, and the reverse movement gear switching unit 20D (20D′) provided between the input shaft 15 and the reverse shaft 18 and formed with the pair of the reverse gear set 27 (27A) and the reverse movement switching clutch 30D that is configured to establish the power transmission path established by the reverse gear set 27 between the input shaft 15 and the reverse shaft 18. The forward movement shift stage gear set 21 a and 21 b of the first forward movement gear switching unit 20A arranged further away from the engine 10 is a gear set for low speed shift stage. The reverse gear set 27 (27A) is formed with the driving gear 27 a (27 a′) provided at the input shaft 15, the driven gear 27 c (27 c′) rotatably supported at the reverse shaft 18 and connected to the rotation of the reverse shaft 18 by the reverse movement switching clutch 30D, and the idler gear 27 b (27 b 1, 27 b 2) rotatably supported at the first counter shaft 16 and engaged with the driving gear 27 a (27 a′) and the driven gear 27 c (27 c′). The driving gear 27 a (27 a′) and the idler gear 27 b (27 b 1) of the reverse gear set 27 (27A) serve also as the 1st shift stage gear set 21 a and 21 b, respectively, arranged more remote from the engine 10 than the 2nd shift stage gear set 22 a and 22 b of the first forward movement gear switching unit 20A. Accordingly, the reverse movement gear switching unit 20D (20D′) provided at the input shaft 15, the first counter shaft 16 and the reverse shaft 18 is not arranged farther from the engine 10 than the 1st shift stage gear set 21 a and 21 b arranged more remote from the engine 10 at first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b. Hence, a size of the cut-out portion 12 b formed at the upper portion of the back wall portion 12 a is not reduced. Therefore, even in the case where the reverse movement gear switching unit 20D (20D′) is provided within the transmission case 12, one of the side frames 13 is provided so as to extend through the cut-out portion 12 b in the front-rear direction of the vehicle, so that one of the side frames 13 does not interfere with the transmission case 12. As a result, the axially connected engine 10 and transmission 11 (11′) is transversely mountable on the vehicle body. Further, as the driving gear 27 a (27 a′) and the idler gear 27 b (27 b 1 ) serve also as the 1st shift stage gear set 21 a and 21 b arranged more remote from the engine 10 at the first forward movement gear switching unit 20A than the 2nd shift stage gear set 22 a and 22 b, one of the plural gears provided within the transmission case 12 is eliminated, which resulting in simplifying the structure of the transmission 11 (11′) and downsizing the transmission 11 (11′). As the 1st shift stage gear set 21 a and 21 b of the first forward movement gear switching unit 20A, serving also as the driving gear 27 a of the reverse gear set 27, is the gear of the low speed shift stage. Hence, the reduction gear ratio of the reverse gear set 27 is easily increased.

According to the embodiments, the idler gear further includes the first idler gear 27 b 1 rotatably supported at the first counter shaft 16 and engaged with the driving gear 27 a′, and the second idler gear 27 b 2, whose diameter is smaller than that of the first idler gear 27 b 1, integrally formed at the first idler gear 27 a′ in an axial direction of the first counter shaft 16 and engaged with the driven gear 27 c′, wherein the driving gear 27 a′ and the first idler gear 27 b 1 of the reverse gear set 27A serve also as the driving gear 21 a and the driven gear 21 b of the 1st shift stage gear set provided at the first forward movement gear switching unit 20A, respectively.

Accordingly, the second idler gear 27 b 2, whose diameter is smaller than the diameter of the first idler gear 27 b 1, is integrally formed at the first idler gear 27 b 1 of the reverse gear set 27A in the axial direction of the first counter shaft 16. The first idler gear 27 b 1 is engaged with the driving gear 27 a′ and the second idler gear 27 b 2 is engaged with the driving gear 27 c′. The diameter of the driven gear 27 c′ may be reduced in a case where the reverse gear set 27A is reduced in two stages, i.e. in a case where the reduction gear ratio of the reverse gear set 27A is determined on the basis of the gear ratio between the driving gear 27 a and the first idler gear 27 b 1 and the gear ratio between the second idler gear 27 b 2 and the driven gear 27 c′. Hence, even in a case where the reverse movement gear switching unit 20D′ is provided within the transmission case 12, the protruding amount of the transmission case 12 from the engine 10 is reduced, so that the transmission 11′ is easily mountable to the vehicle body.

According to the embodiments, the first forward movement gear switching unit 20A includes the 1st shift stage gear set 21 a and 21 b, the 2nd shift stage gear set 22 a and 22 b and the first switching clutch 30A arranged therebetween and establishing the power transmission path established by each of the 1st shift stage gear set and the 2nd shift stage gear set between the input shaft 15 and the first counter shaft 16, the second forward movement gear switching unit 20B includes the 3rd shift stage gear set 23 a and 23 b, the 4th shift stage gear set 24 a and 24 b and the second switching clutch 30B arranged therebetween and establishing the power transmission path established by each of the 3rd shift stage gear set and the 4th shift stage gear set between the input shaft 15 and the second counter shaft 17, and the third forward movement gear switching unit 20C includes the 5th shift stage gear set 25 a and 25 b, the 6th shift stage gear set 26 a and 26 b and the third switching clutch 30C arranged therebetween and establishing the power transmission path established by each of the 5th shift stage gear set and the 6th shift stage gear set between the input shaft 15 and the second counter shaft 17.

Accordingly, the first forward movement gear switching unit 20A includes the 1st shift stage gear set 21 a, 21 b, the 2nd shift stage gear set 22 a, 22 b, and the first switching clutch 30A that is provided between the 1st shift stage gear set 21 a, 21 b and the 2nd shift stage gear set 22 a, 22 b and establishes the power transmission path established by each of the 1st shift stage gear set 21 a, 21 b and 2nd shift stage gear set 22 a, 22 b between the input shaft 15 and the first counter shaft 16. The second forward movement gear switching unit 20B includes the 3rd shift stage gear set 23 a, 23 b, 4th shift stage gear set 24 a, 24 b, and the second switching clutch 30B that is provided between the 3rd shift stage gear set 23 a, 23 b and the 4th shift stage gear set 24 a, 24 b and establishes the power transmission path established by each of the 3rd shift stage gear set 23 a, 23 b and the 4th shift stage gear set 24 a, 24 b between the input shaft 15 and the second counter shaft 17. The third forward movement gear switching unit 20C includes the 5th shift stage gear set 25 a, 25 b, the 6th shift stage gear set 26 a, 26 b, and the third switching clutch 30C that is provided between the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b and establishes the power transmission path established by each of the 5th shift stage gear set 25 a, 25 b and the 6th shift stage gear set 26 a, 26 b between the input shaft 15 and the second counter shaft 17. Accordingly, the transmission 11 (11′) has the six shift stages, which is the maximum number of shift stages for a transmission having three forward movement gear switching units. Hence, the output torque of the transmission 11 (11′) is increased.

The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby. 

1. A vehicle comprising: an engine; a pair of side frames provided at the vehicle so as to extend along both sides of a vehicle body in a front-rear direction of the vehicle; a transmission adapted to be axially connected with the engine and adapted to be transversely mounted on the vehicle body, including: an input shaft adapted to be rotatably driven by the engine; an output shaft connected to a driving wheel; a first counter shaft arranged in parallel to the input shaft and connected to the output shaft; a second counter shaft arranged in parallel to the input shaft and connected to the output shaft; a first gear mechanism between the input shaft and the first counter shaft, the first gear mechanism having a first gear set, a second gear set and a first switching clutch provided between the first and second gear sets to selectively establish a power transmission path between the input shaft and the first counter shaft via either the first gear set or the second gear set; a second gear mechanism between the input shaft and the second counter shaft, the second gear mechanism having a third gear set, a fourth gear set and a second switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the third gear set or the fourth gear set; a third gear mechanism between the input shaft and the second counter shaft, the second and third gear mechanisms extending in parallel with one another between the input shaft and the second counter shaft, the third gear mechanism having a fifth gear set, a sixth gear set and a third switching clutch for selectively establishing a power transmission path between the input shaft and the second counter shaft via the fifth gear set or the sixth gear set; and a transmission case supporting and covering most of the input shaft, the first counter shaft, the second counter shaft, the output shaft, the first gear mechanism, the second gear mechanism and the third gear mechanism; wherein the first gear mechanism and the second gear mechanism are arranged relatively close to the engine, the third gear mechanism is arranged at a position more remote from the engine than the second gear mechanism, and the first counter shaft is arranged above the input shaft and the second counter shaft, a driving gear of the second gear set, serves also as a driving gear of the third gear set and is axially aligned with the ends of the second and third gear sets closer to the engine, and a driving gear of the first gear set is arranged at an axial distance from the engine substantially corresponding to the axial location of the third switching clutch, and wherein the transmission case includes a back wall portion formed with a first back wall portion corresponding to the second gear mechanism and the third gear mechanism and a second back wall portion corresponding to the first gear mechanism and located closer to the engine than the first back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion, and wherein the transmission is connected to the engine and transversely mounted on the vehicle body so that one of the pair of the side frames extending along the both sides of the vehicle body in the front-rear direction thereof extends through the cut-out portion.
 2. The vehicle according to claim 1, further comprising: a reverse movement switching gear mechanism including a reverse shaft arranged in parallel to the input shaft and connected to the output shaft, a reverse gear set provided between the input shaft and the reverse shaft and a reverse movement switching clutch establishing a power transmission path established by the reverse gear set between the input shaft and the reverse shaft, wherein the first gear set of the first gear mechanism is positioned more remotely from the engine than the second gear set and is a gear set for a low speed shift stage, and the reverse movement gear mechanism includes a driving gear provided at the input shaft, a driven gear rotatably supported at the reverse shaft and tolerably connectable to the reverse shaft by means of the reverse movement switching clutch and an idler gear rotatably supported at the first counter shaft and engaged with the driving gear and the driven gear, wherein the driving gear and the idler gear of the reverse gear set serve also as a driving gear and a driven gear of the first gear set respectively, of the first gear mechanism.
 3. The vehicle according to claim 2, wherein the idler gear further includes a first idler gear rotatably supported at the first counter shaft and engaged with the driving gear, and a second idler gear, whose diameter is smaller than that of the first idler gear, integrally formed with the first idler gear but spaced therefrom in the axial direction of the first counter shaft and engaged with the driven gear, wherein the driving gear and the first idler gear of the reverse gear set serve also as the driving gear and the driven gear, respectively, of the first gear set provided at the first gear mechanism.
 4. The vehicle according to claim 3, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween to selectively establish either a first speed range power transmission path or a second speed range power transmission path between the input shaft and the first counter shaft, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween to selectively establish either a third speed range power transmission path or a fourth speed range power transmission path between the input shaft and the second counter shaft, and the third gear mechanism includes the fifth gear set, the sixth forward movement shift stage gear set and the third switching clutch arranged therebetween to selectively establish either a fifth speed range power transmission path or a sixth speed range power transmission path between the input shaft and the second counter shaft.
 5. The vehicle according to claim 2, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween to selectively establish either a first speed range power transmission path or a second speed range power transmission path between the input shaft and the first counter shaft, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween to selectively establish either a third speed range power transmission path or a fourth speed range power transmission path between the input shaft and the second counter shaft, and the third gear mechanism includes the fifth gear set, the sixth forward movement shift stage gear set and the third switching clutch arranged therebetween to selectively establish either a fifth speed range power transmission path or a sixth speed range power transmission path between the input shaft and the second counter shaft.
 6. The vehicle according to claim 1, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween to selectively establish either a first speed range power transmission path or a second speed range power transmission path between the input shaft and the first counter shaft, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween to selectively establish either a third speed range power transmission path or a fourth speed range power transmission path between the input shaft and the second counter shaft, and the third gear mechanism includes the fifth gear set, the sixth forward movement shift stage gear set and the third switching clutch arranged therebetween to selectively establish either a fifth speed range power transmission path or a sixth speed range power transmission path between the input shaft and the second counter shaft.
 7. A transmission adapted to be axially connected with an engine and adapted to be transversely mounted on a vehicle body, comprising: an input shaft adapted to be rotatably driven by the engine; an output shaft connected to a driving wheel; a first counter shaft arranged in parallel to the input shaft and connected to the output shaft; a second counter shaft arranged in parallel to the input shaft and connected to the output shaft; a first gear mechanism between the input shaft and the first counter shaft, the first gear mechanism having a first gear set, a second gear set and a first switching clutch provided between the first and second gear sets to selectively establish a power transmission path between the input shaft and the first counter shaft via either the first gear set or the second gear set; a second gear mechanism between the input shaft and the second counter shaft, the second gear mechanism having a third gear set, a fourth gear set and a second switching clutch to selectively establish a power transmission path between the input shaft and the second counter shaft via the third gear set or the fourth gear set; a third gear mechanism between the input shaft and the second counter shaft, the second and third gear mechanisms extending in parallel with one another between the input shaft and the second counter shaft, the third gear mechanism having a fifth gear set, a sixth stage gear set and a third switching clutch provided between the fifth and sixth gear sets to selectively establish a power transmission path between the input shaft and the second counter shaft via the fifth gear set or the sixth gear set; and a transmission case supporting and covering most of the input shaft, the first counter shaft, the second counter shaft, the output shaft, the first gear mechanism, the second gear mechanism and the third gear mechanism; wherein the first gear mechanism and the second gear mechanism are arranged relatively close to the engine, the third gear mechanism is arranged at a position more remote from the engine than the second gear mechanism, and the first counter shaft is arranged above the input shaft and the second counter shaft, a driving gear of the second gear set serves also as a driving gear of the third gear set and is axially aligned with the ends of the second and third gear sets closer to the engine, and a driving gear of the first gear set is arranged on the input shaft at an axial distance from the engine substantially corresponding to the axial location of the third switching clutch, and wherein the transmission case includes a back wall portion formed with a first back wall portion corresponding to the second gear mechanism and the third gear mechanism and a second back wall portion corresponding to the first gear mechanism and located closer to the engine than the first back wall portion, thereby forming a cut-out portion at an upper portion of the back wall portion.
 8. The transmission according to claim 7, further comprising: a reverse movement gear mechanism including a reverse shaft arranged in parallel to the input shaft and connected to the output shaft, a reverse gear set provided between the input shaft and the reverse shaft and a reverse movement switching clutch establishing a power transmission path established by the reverse gear set between the input shaft and the reverse shaft, wherein the first gear set of the first gear mechanism is positioned more remotely from the engine than the second gear set and is a gear set for a low speed shift stage, and the reverse movement gear mechanism includes a driving gear provided at the input shaft, a driven gear rotatably supported at the reverse shaft and rotatably connectable to the reverse shaft by means of the reverse movement switching clutch and an idler gear rotatably supported at the first counter shaft and engaged with the driving gear and the driven gear, wherein the driving gear and the idler gear of the reverse gear set serve also as a driving gear and a driven gear of the first gear set respectively, of the first gear mechanism.
 9. The transmission according to claim 8, wherein the idler gear further includes a first idler gear rotatably supported at the first counter shaft and engaged with the driving gear and, a second idler gear, whose diameter is smaller than that of the first idler gear, integrally formed with the first idler gear but spaced therefrom in the axial direction of the first counter shaft and engaged with the driven gear, wherein the driving gear and the first idler gear of the reverse gear set serve also as the driving gear and the driven gear, respectively, of the first gear set provided at the first gear mechanism.
 10. The transmission according to claim 9, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween to selectively establish either a first speed range power transmission path or a second speed range power transmission path between the input shaft and the first counter shaft, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween to selectively establish either a third speed range power transmission path or a fourth speed range power transmission path between the input shaft and the second counter shaft, and the third gear mechanism includes the fifth gear set, the sixth gear set and the third switching clutch arranged therebetween to selectively establish either a fifth speed range power transmission path or sixth speed range power transmission path between the input shaft and the second counter shaft.
 11. The transmission according to claim 8, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween to selectively establish either a first speed range power transmission path or a second speed range power transmission path between the input shaft and the first counter shaft, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween to selectively establish either a third speed range power transmission path or a fourth speed range power transmission path between the input shaft and the second counter shaft, and the third gear mechanism includes the fifth gear set, the sixth gear set and the third switching clutch arranged therebetween to selectively establish either a fifth speed range power transmission path or sixth speed range power transmission path between the input shaft and the second counter shaft.
 12. The transmission according to claim 7, wherein the first gear mechanism includes the first gear set, the second gear set and the first switching clutch arranged therebetween to selectively establish either a first speed range power transmission path or a second speed range power transmission path between the input shaft and the first counter shaft, the second gear mechanism includes the third gear set, the fourth gear set and the second switching clutch arranged therebetween to selectively establish either a third speed range power transmission path or a fourth speed range power transmission path between the input shaft and the second counter shaft, and the third gear mechanism includes the fifth gear set, the sixth gear set and the third switching clutch arranged therebetween to selectively establish either a fifth speed range power transmission path or sixth speed range power transmission path between the input shaft and the second counter shaft. 